They probably have a nest near where you're walking and are trying to protect it and their eggs or young. In a few short weeks, the baby robins will be out of the nest, so I'd just try to give them as much space as possible and enjoy the fact that they chose your yard as the place they want to raise their babies. Oh, and you don't have to worry...the robins will try to chase you, but they won't cause any harm. :-)